St. Irenaeus

St. Irenaeus (2nd cenutry C.E. – c. 202) was Bishop of Lugdunum in Gaul, then a part of the Roman Empire (now Lyon, France). He was an early church father and apologist, and his writings were formative in the early development of Christian theology. Irenaeus' best-known book, Adversus Haereses or Against Heresies (c. 180) is a detailed attack on Gnosticism, which was then a serious threat to the Church, and especially on the system of the Gnostic Valentinus.